Biometric image capturing apparatus and biometric image capturing method

Abstract

A biometric image capturing apparatus includes an irradiating unit configured to irradiate a subject with light, a camera configured to capture an image of the subject, a polarizing unit which is disposed on an optical path between the irradiating unit and the camera, and configured to allow passage of light in a first polarization direction and light in a second polarization direction, a processor configured to perform computation using a first image captured by the camera according to the light in the first polarization direction that has passed through the polarizing unit and a second image captured by the camera according to the light in the second polarization direction that has passed through the polarizing unit, and to determine whether the subject is a biological body according to a result of the computation performed by the computing unit.

What is claimed is: 
     
       1. A biometric image capturing apparatus comprising:
 an illuminating apparatus which irradiates a subject with light; 
 a camera configured to capture an image of the subject; 
 a first polarizing filter, disposed on a first optical path between the illuminating apparatus and the subject, which allows passage of the light from the illuminating apparatus onto the subject; 
 a second polarizing filter, disposed on a second optical path between the subject and the camera, which allows passage of the light reflecting from the subject in a first polarization direction and in a second polarization direction, the first and second polarization directions being different; and 
 a processor configured to
 perform a computation to obtain a difference between a pixel value of each pixel of a first image, captured by the camera according to the light in the first polarization direction that has passed through the second polarizing filter, and a corresponding pixel value of each pixel of a second image captured by the camera according to the light in the second polarization direction that has passed through the second polarizing filter, 
 generate a difference image from the difference between each pixel of the first and second images, 
 generate a plurality of edge images indicating edges for a plurality of directions by performing edge detection on the difference image using a plurality of filters detecting the edges for the plurality of directions, 
 calculate a sum of pixel values of pixels for each of the plurality of edge images, 
 calculate, as a total edge amount, a total of sums of the pixel values calculated for the plurality of the edge images, and 
 determine the subject is a biological body according to the total edge amount being equal to or greater than a threshold. 
 
 
     
     
       2. The biometric image capturing apparatus according to  claim 1 , wherein the first polarization direction and the second polarization direction are orthogonal to each other. 
     
     
       3. The biometric image capturing apparatus according to  claim 1 , wherein the second polarizing filter is rotatable and provides a polarization direction settable in accordance with a rotation angle. 
     
     
       4. A biometric image capturing method comprising:
 irradiating, by an illuminating apparatus, a subject with light; 
 capturing, by a camera, an image of the subject; 
 performing a computation by a processor to obtain a difference between a pixel value of each pixel of a first image, captured by the camera according to light in first polarization direction that has passed through a first polarizing filter disposed on a first optical path between the illuminating apparatus and the subject and through a second polarizing filter, disposed on a second optical path between the subject and the camera, and a corresponding pixel value of each pixel of a second image captured by the camera according to light in a second polarization direction that has passed through the second polarizing filter; 
 generating a difference image from the difference between each pixel of the first and second images; 
 generating a plurality of edge images indicating edges for a plurality of directions by performing edge detection on the difference image using a plurality of filters detecting the edges for the plurality of directions; 
 calculating a sum of pixel values of pixels for each of the plurality of edge images, 
 calculating, as a total edge amount, a total of sums of the pixel values calculated for the plurality of edge images, and 
 determine the subject is a biological body according to the calculated total edge amount being equal to or greater than a threshold. 
 
     
     
       5. The biometric image capturing method according to  claim 4 , wherein the first polarization direction and the second polarization direction are orthogonal to each other. 
     
     
       6. The biometric image capturing method according to  claim 4 , wherein the second polarizing filter is rotatable and provides a polarization direction settable in accordance with a rotation angle.